The research described herein includes synthesis, spectroscopy, and quantum chemical calculations with focus on the characteristic properties of compounds with bonds between carbon and the heavier Group 14 elements. The chapters based on the first four papers concern σ- and σ/π-conjugated compounds, although the focus of the first paper is on ring strain of bicyclo[1.1.1]pentanes with C, Si, Ge or Sn at the bridgeheads. The relationship between calculated homodesmotic ring strain energies and through-space distances between the bridgehead atoms was evaluated, and it was found that replacing one of the methylene bridges with phospha-methyl gave both low strain and short through-space distance. Two kinds of σ/π-interacting systems were analysed with the difference that the σ- and π-bonded segments were either allowed to rotate freely relative each other or frozen into a conformer with maximal σ/π-interaction. The freely rotating systems are star-shaped oligothiophenes linked by heavy alkane segments. Density functional theory (DFT) calculations of hole reorganization energies support the measured hole mobilites. In summary, longer central oligosilane linkages, when compared to shorter, facilitate intermolecular hole-transfer between oligothiophene units. In 1,4-disilacyclohexa-2,5-dienes, the strength of the π- and pseudo-π interaction depends on the substituents at Si. Vapour phase UV absorption spectroscopy of 2,3,5,6-tetraethyl-1,1,4,4-tetrakis(trimethylsilyl)-1,4-disilacyclohexa-2,5-diene reveals a strong absorption at 273 nm (4.50 eV). Time-dependent DFT calculations further indicate that octastannylated 1,4-disilacyclohexa-2,5-diene has is lowest excited state at 384 nm (3.23 eV). The electronic, geometric and optical properties of substituted 1,4-disilacyclohexa-2,5-dienes were compared with those of the correspondingly substituted siloles. It was found that the lowest excitations of siloles are less tunable than those of 1,4-disilacyclohexa-2,5-dienes. The final section concerns strongly reverse-polarised 2-amino-2-siloxysilenes formed thermally from carbamylpolysilanes, and their lack of reaction with alcohols. Instead, the carbamylsilane reacts with alcohols giving silyl ethers, leading to a new benign route for alcohol protection.

The present thesis deals with a theoretical description of issues regarding chemical bonding, structure and stability of transition metal carbides and multilayered structures. First principles density functional theory has been used extensively to investigate the properties of alloyed solutions of transition metal carbides. Joint theoretical and experimental investigations have shown that there is a driving force for carbon to be released from these ternary carbide systems as a response to the alloying. This release of carbon was shown to yield favorable lubricating properties in the case of alloyed solutions of Ti-Al-C, that were not present in the case of pure TiC, a property that can be used to design new materials that combine high hardness with favorable tribological properties. From calculations of the activation energy of C diffusion in the vicinity of substitutional transition metal impurities (M) in TiC, it is found that the mobility of C atoms is increased due to the presence of the impurities. The lowering of the activation energy barriers suggests that the mobility of C in alloyed solutions of Ti-M-C is increased and will be more pronounced at lower temperature than for C diffusion in TiC. The magnetic properties of alloyed solutions of Ti-Fe-C has been investigated using both theory and experiment. Theoretical calculations reveal that the magnetic moment and the critical temperature increase when increasing the Fe content as well as when lowering the C content in the system. Furthermore, the magnetic exchange parameters between Fe atoms were found to clearly reflect changes in the chemical bonding when varying the C content. Experimentally the magnetic properties were found to be rather substantial. Furthermore, the magnetic properties changes upon annealing due to the formation of Fe-rich and Fe-poor regions in the system. After long enough annealing times precipitates of α-Fe are formed which is consistent with theoretical predictions. The interaction between TiC(111) surfaces and C in the form of graphite has also been investigated. For these systems it was found that graphite was rather strongly bonded to the carbide surface and that the atomic as well as electronic structure at the interface depend on the termination of the carbide surface. This research was motivated by the recent interest in graphene, but also to investigate how carbide grains interacts with C when dispersed in a carbon matrix. A model for the calculation of structural parameters in multilayer structures has been presented and evaluated. The model is based on classical elasticity theory and uses the elastic constants of the materials constituting the multilayer as the only input.

The nature of interactions within a molecule, i.e. chemical bonding, is well understood today. However, our understanding about intermolecular interactions, which has great relevance in nature, is still evolving. Historically there are two types of intermolecular interactions, van der Waals interaction and hydrogen bonding. However, there has been an upsurge of interest in the halogen bonding and lithium bonding during the last decade. The main emphasis of our research is to understand these interactions in detail, in particular non-conventional hydrogen bond acceptors. In this work, weakly bound complexes are studied using Pulsed Nozzle Fourier Transform Microwave Spectrometer, which has been fabricated in our laboratory and various theoretical methods. FTMW spectroscopy in the supersonic beam provides accurate structural information about the near-equilibrium geometry of small dimers and trimers in isolation. The home-built Pulsed Nozzle Microwave spectrometer, having a spectral range of 2-26.5 GHz has been used to record the microwave spectrum of these complexes. The spectrometer consists of a Fabry-Perot cavity, electronic circuit and pumps. Fabry-Perot cavity is the interaction zone of the molecules and radiation. The electronic circuit is used for the polarization and detection of the signal. Mechanical and diffusion pumps are used to maintain the vacuum inside the cavity. The gas molecules of interest are then mixed with a carrier gas and pulsed supersonically inside the cavity through a nozzle of 0.8 mm diameter. The emission from the complexes formed during the expansion is detected by super-heterodyne detection technique and then Fourier transformed. The first chapter of the thesis gives a brief introduction to intermolecular interactions, hydrogen bonding, halogen bonding, lithium bonding and molecular 2 of clusters. The chapter also includes a brief introduction to rotational spectroscopy. The second chapter of the thesis discusses the experimental and theoretical methods. It includes a detailed discussion of the mechanical and electrical parts of the spectrometer and the software used, which is developed in Labview 7.1. The various theoretical methods (ab initio and DFT) and the basis sets are discussed along with Atoms In Molecules Theory and the criteria used to characterize hydrogen bond. In the third chapter, to understand the ability of saturated hydrocarbons to act as hydrogen bond donor and acceptor, interaction of CH4 with H2S is studied using rotational spectroscopy as well as theoretical methods such as ab initio and Atoms In Molecules theory. Three progressions were obtained for the CH4•••H2S complex using microwave spectroscopy. The progressions were independently fitted to a linear top Hamiltonian. Absence of J10 transition in Progression II confirms the presence of higher internal angular momentum state, m=1. This also confirms the internal rotation of the monomers in the complex. Progressions II and III have negative centrifugal distortion constants. Hence both the states are from some excited internal rotation/torsional motion with strong vibrational-rotational coupling. The moment of inertia obtained from the experimental rotational constant confirms the structure in which sulphur of H2S is close to CH4. This also supports the structure in which CH4 is the hydrogen bond donor, if such an interaction is present. AIM analysis and the potential energy barrier for internal rotation show orientational preference and hence hydrogen bonding. The ab initio results show that CH4•••HSH interaction is more favorable than CH3H•••SH2. Ab initio and AIM studies also gave a structure where there is direct interaction between C and S. This is interesting since the electronegativities of C and S are comparable. Experimentally obtained negative distortion constants for the other two states, confirm excited state rotational-vibrational coupling. The experimental data give a floppy structure having internal rotation. In the fourth chapter the complex chosen for investigation is benzene-ethylene. Experiments in condensed phase and theoretical works show evidence of - stacking in benzene dimer, but there is no gas phase spectroscopic evidence available for the same. The lack of permanent dipole moment in the -stacked geometry of benzene dimer is the hindrance in the experimental observation of the same using microwave spectroscopy. Substitution of one of the benzene with ethylene in the -stacked structure will result in a complex having permanent dipole moment. C6H6 C2H4 complex can have, in addition to -stacking, C-H/interaction. There could be a competition between C6H6 and C2H4, either of which can act as H-bond donor. Experiments show the evidence of C-H/interaction, where C2H4 is the hydrogen bond donor. To ascertain hydrogen bond interaction AIM analysis has been carried out. The results show C-H/interaction, where one of the C2H4 hydrogen interacts with the benzene. Even though the aim was to get the -stacked geometry, it could not be obtained. However theory and AIM supports the formation of -stacked complex. In the fifth chapter using theoretical methods the ability of radicals as acceptor of hydrogen, lithium and chlorine bonds are examined with CF3 radical as the model system. As hydrogen bonds are highly sensitive to the environment, the effect of substitution of hydrogen by fluorine is also analyzed. It is found that, even though CH3 and CF3 radicals are topologically different, they interact in a similar fashion. AIM analysis of CF3HY satisfies all the eight criteria proposed by Koch and Popelier for hydrogen bonding. Here the hydrogen bond formed is charge transfer assisted. The interaction energies of the complexes are inversely proportional to the dipole moment of hydrogen bond donors and are proportional to the charge transfer occurring in the complex. Interaction energies from ab initio calculations confirm complexation of CF3 radical with LiY(Y=F, Cl, Br) and ClF. AIM analysis of CF3LiY and CF3ClF complexes show a bond critical point between Li/Cl and the C of CF3 and the condition of mutual penetration is also met. In CF3LiY complexes the interaction energies and charge transferred are directly proportional to the dipole moment of the Li bond donor. In the sixth chapter in order to extend the concept of non-conventional hydrogen bond acceptors to transition metals, complexes of Fe (Fe(CO)5) with HX (X=F,Cl,Br) have been studied theoretically. DFT calculations show that the structure in which the hydrogen of HX interacting with Fe through the sixth co-ordination site is a stable geometry. AIM analysis shows the presence of a bond critical point between the iron and the hydrogen of HX and hence bond formation. Q obtained from NBO analysis shows that there is charge transfer from the organometallic system to the hydrogen bond donor. However the interaction energies of the complexes are proportional to the dipole moment of hydrogen bond donors and are inversely proportional to the charge transfer for these complexes. H-bonding leads to the stabilization of square pyramidal geometry. ‘Hydrogen bond radius’ of iron has also been defined. Studies on the interaction of Fe(CO)5 with ClF and ClH showed that Fe can also act as a chlorine bond acceptor. Seventh chapter provides the overall conclusion and also discusses future direction.

In this study, we used UV-ozone Ar sputtering, X-ray photoelectron and ultra-violet photoelectron spectroscopies and sputtering based depositions of RuO2 and Se nano-layers on indium tin oxides (ITOs). We elucidated the effect of Ar sputtering on the composition and chemistry of Sn rich ITO surface. We demonstrated that while a combination of UV-ozone radiation and Ar sputtering removes most of the hydrocarbons responsible for degrading the work function of ITO, it also removes significant amount of the segregated SN at the ITO surface that's responsible for its reasonable work function of 4.7eV. We also demonstrated for the first time that sputtering cleaning ITO surface leads to the reduction of the charge state of Sn from Sn4+ to Sn2+ that adds to the degradation of the work function. For the nano-layers coverage of ITO studies, we evaluated both RuO2 and Se. For RuO2 coated ITO, XPS showed the formation of a Ru-Sn-O ternary oxide. The RuO2 nano-layer reduced the oxidation state of Sn in the Sn-rich surface of ITO from +4 to +2. The best work function obtained for this system is 4.98eV, raising the effective work function of ITO by more than 0.5 eV. For the Se coated ITO studies, a systematic study of the dependence of the effective work function on the thickness of Se overage and its chemistry at the Se/ITO interface was undertaken. XPS showed that Se reacts with Sn at the Sn-rich surface of ITO determined the presence of both negative and positive oxidation state of Se at the Se/ITO interface. The Se also reduced the oxidation state of Sn from Sn4+ to Sn2+ in the Sn-rich ITO surface. The highest effective work function obtained for this system is 5.06eV. A combination of RuO2/Se nanoscale coating of optimally cleaned ITO would be a good alternative for device applications that would provide work function tuning in addition to their potential ability to act as interface stabilizers and a barrier to reaction and inter-diffusion at ITO/active layers interfaces responsible for long term stability of devices and especially organic solar cells and organic light emitting diodes.

The main focus of this work was to investigate substitution effects on the chemical bonding in compounds of AlB 2 -type and related structure types. Delocalization indices within the QTAIM approach and the topological analysis of the ELI functionals were used as tools to describe the bonding situation in digallides and diborides. Digallides of AlB 2 -type were found only within group I and II; for CaGa 2 (meta-stable phase), SrGa 2 , BaGa 2 , YGa 2 and LaGa 2 compounds. Within these compounds, QTAIM analysis showed similar trend as previously found in diborides. That is, along the period in the Periodic Table, metal-triel interactions increase at the expense of in-plane (triel-triel) ab interactions (Tr=triel). However, transition metal diborides adopt the AlB 2 -type up to group VI. To understand this difference, we simulated transition metal (TM) digallides and diborides up to group VI in the AlB 2 -type. Additionally, the puckered variants diborides ReB 2 and OsB 2 were also simulated in the AlB 2 -type. With filling of d shell, there is a delicate balance between increase of TM–Tr and decrease of in-plane (Tr–Tr) ab electron sharing. This balance is maintained as long as interlayer interactions in the c direction (Tr–Tr ) c and (TM–TM ) c are not relatively too high in comparison to in-plane electron sharing. In contrast to TM B 2 of AlB 2 -type, digallides in the same structure type build up strong interlayer interactions for early transition metal elements. Our results showed that within digallides, a relatively strong increase in interlayer electron sharing (Ga–Ga) c and (TM–TM ) c takes place. Such increase occurs already for ScGa 2 and TiGa 2 . On the other hand, diborides show a steady increase in electron sharing of TM –B and (TM–TM ) c , but not of (B–B) c . Therefore, it is reasonable to suggest that diborides will tend to adopt a 3D network composed of boron and transition metal atoms (ReB 2 and RuB 2 types). The additional high (Ga–Ga) c interlayer interactions indicate a tendency for digallides to form 3D networks composed only by gallium atoms, characteristic of CaGa 2 (CaIn 2 -type) and ScGa 2 (KHg 2 -type). The counterbalancing bonding effects of in-plane and out-of-plane interactions that give the chemical flexibility of the AlB 2 -type in diborides is thus disrupted in AlB 2 -type digallides by a further enhanced degree of interlayer interactions (Ga–Ga) c and (TM –TM ) c . This results in a smaller number of digallides than that of diborides in AlB 2 -type. The most conspicuous difference between diborides and digallides of AlB 2 -type is in the representation of the B – B and Ga – Ga bonds revealed by the ELI- D topology. Whereas AlB 2 -type diborides exhibit one ELI-D attractor at the B – B midpoint, AlB 2 -type digallides exhibit two ELI-D attractors symmetrically opposite around the Ga – Ga bond midpoint. We utilized the E 2 H 4 (E=triel, tetrel ) molecular series in the D 2h point group symmetry as model systems for solid state calculations. In particular, we addressed the appearance of ELI- D double maxima for Ga – Ga, by using orbital decomposition within the ELI framework. The ELI-D topology changes along the 13th group T r 2 H 4 series. Whereas B 2 H 4 and Al 2 H 4 exhibit one ELI-D attractor representing the Tr–Tr bond, Ga 2 H 4 and In 2 H 4 give rise to two ELI-D attractors. Partial ELI-D allows the orbital decomposition of the electron density. Partial ELI-q gives access to the decomposition of a two-particle property, which is given by the Fermi-hole curvature. We have found that the d-orbitals enable the formation of the two ELI-D attractors through pairing contributions. This has a net effect of lowering electron localizability at the Ga – Ga bond midpoint. Namely, the different ELI-D topology of Ga – Ga and B – B bonds stems from the contributions of d-orbitals to orbital pairing. We have also investigated the bonding situation in transition metal diborides of ReB 2 -type (MnB 2 , TcB 2 , ReB 2) and RuB 2 -type (OsB 2 , RuB 2). One can consider these two structure types as an extension of the trend found in TM B 2 of AlB 2 -type: an increase in TM –B interactions and an enhanced three-center bonding. The change in the structure type results in a puckered layer of boron atoms with electrons equally shared between B – B and TM –B. However, TM –B bonds exhibit a high three-center character. The ELI-D/QTAIM intersection technique also revealed a high participation of TM in the B – B bonding basin population. Moreover, ELI-D topology in the ReB 2 -type also discloses a seemingly important Re 3 three-center interaction along the flat layer of Re atoms. Such basin is absent in MnB 2 , which coincides with the fact that MnB 2 was only observed in the AlB 2 -type. In this regard, we concluded that the 3D network consists not only of covalent B – B bonds, but also of TM –B bonds.

Vid ett laborativt arbete i undervisningen får eleverna möjlighet att samtala med varandra och dela med sig av tidigare erfarenheter, vilket har en positiv effekt på elevernas lärande. Att skriva i undervisningen har också visat sig ha en stor effekt på elevernas lärande, då de får utveckla och strukturera om sina tankar. Syftet med denna studie har varit att undersöka hur elevernas kunskap inom kemisk bindning utvecklas, samt hur elevernas språk utvecklas vid kursmoment med laborativt inslag och laborationsrapportskrivning. För att undersöka detta har kommunikationen hos fyra elever, som gick första året på gymnasiet och läste kemi, spelats in och sedan transkriberats, när eleverna genomförde och efteråt presenterade en laboration. Det här materialet tillsammans med elevernas laborationsrapporter blev sedan analyserade dels med PEA, dels med fokus på ämnesspråk och vardagsspråk. Resultatet visar att under alla delar i kursmomenten finns det ett fokus på laborationsrapporten och hur den ska skrivas där eleverna får möjlighet att utveckla sina kunskaper inom kemisk bindning samt utveckla sitt ämnesspråk. / Laboratory work in science education gives students opportunity to have a conversation and share knowledge with other classmates, which have a positive effect on students learning. To be able to communicate by writing in science education, has also been proven to have an enhanced the learning process by helping students to organized and challenged their thoughts. Therefore, this study objective is to explore how students’ knowledge about chemical bonding and their scientific language develops with laboratory work and laboratory report writing. To explore this, the communication of four students in their first year of high school, studying chemistry were recorded and later transcribed, while they performed and afterwards presented a lab. This material together with the students’ final laboratory report has been analyzed with regards to PEA and the language used by students. The study indicates that the use of laboratory report writing has helped students to develop their knowledge about chemical bonding, but also their scientific language.

The main purpose of the study was to compare the effectiveness of multiple intelligences theory based instruction (MITBI) and traditional science instruction (TSI) on 9th grade students&amp / #8217 / understanding of chemical bonding concept and attitudes toward chemistry. In the study, 50 ninth grade students from two classes of Gen&ccedil / Osman high school in Ankara were used. 25 of the students were assigned as experimental group and the other 25 as control group. They were instructed by the same teacher. The study was conducted during May of 2005. The groups were selected from eight 9th grade classes of Gen&ccedil / Osman High School randomly. The students are at the ages between 14 and 16. The group which was assigned as experimental group was instructed by multiple intelligences theory based instruction (MITBI) whereas the other group was traditionally instructed. This experimental study took a period of three weeks. To determine the effectives of multiple intelligences based instruction over traditional science instruction, an achievement test about chemical bonding concept which consisted of 25 items were administered and an attitude scale toward chemistry developed by Geban et al., was applied. Science Process Skill Test was administered to investigate the relationship between the students&amp / #8217 / science process skills and their achievement. For the statistical analysis, t-test, and Analysis of Covariance (ANCOVA) were used. The results showed that students who were instructed by multiple intelligences theory based instruction were achieved higher than the ones which were instructed by the traditional science instruction about chemical bonding concept. There was also a significant difference between the students instructed with Multiple Intelligences Theory Based Instruction (MITBI) and the students instructed with traditional science instruction (TSI) with respect to the attitudes of students toward chemistry. There was no significant difference between the attitudes and achievement of female students and that of male students. Students&amp / #8217 / science process skills had no greater contribution to their success.

The main purpose of this study was to investigate the effects of conceptual change oriented instruction accompanied with analogies on eight grade students&rsquo / understanding of chemical bonding concepts. In addition, the effect of instruction on students&rsquo / attitude toward science as a school subject and the effect of gender difference on understanding of chemical bonding concepts were investigated. Fifty eight-grade students from two classes of a science course taught by the same teacher in B&uuml / y&uuml / kel&ccedil / i Nazim Belger Primary School in the 2010-2011 spring semesters participated in the study. The study included two groups which were selected randomly throughout three classes. One of the groups was defined as control group in which students were instructed by traditionally designed science instruction, while other group was defined as experimental group in which students were instructed by conceptual change texts oriented instruction accompanied with analogies. Chemical Bonding Concept Pre-Test was administered to both groups as a pre-test and Chemical Bonding Concept Post-Test was administered to both groups as a post-test in order to assess their understanding of concepts related to chemical bonding. Students were also given Attitude Scale Towards Science as a School Subject at the beginning and end of the study to determine their attitudes and Science Process Skill Test was used at the beginning of the study to measure their science process skills. The hypotheses were tested by using analysis of covariance (ANCOVA) and two-way analysis of variance (ANOVA). The results indicated that instruction based on constructivist approach caused a significantly better acquisition of scientific conceptions related to chemical bonding and produced significantly higher positive attitudes toward science as a school subject than the traditionally designed science instruction. Also, science process skill was a strong predictor in understanding the concepts related to chemical bonding. On the other hand, no significant effect of gender difference on understanding the concepts about chemical bonding and students&rsquo / attitudes toward science as a school subject was found.

The main purpose of this study was to compare the effectiveness of instruction based on constructivist approach over traditionally designed chemistry instruction on ninth grade students&amp / #65533 / understanding of chemical bonding concepts. In addition, the effect of instruction on students&amp / #65533 / attitude toward chemistry as a school subject and the effect of gender difference on understanding of chemical bonding concepts were investigated. Forty-two ninth grade students from two classes of a chemistry course taught by the same teacher in METU Development Foundation Private School 2000-2001 spring semester were enrolled in the study. The classes were randomly assigned as control and experimental groups. Students in the control group were instructed by traditionally designed chemistry instruction whereas students in the experimental group were taught by the instruction based on constructivist approach. Chemical Bonding Concept Test was administered to both groups as a pre-test and post-test in order to assess their understanding of concepts related to chemical bonding. Students were also given Attitude Scale Toward Chemistry as a School Subject at the beginning and end of the study to determine their attitudes and Science Process Skill Test at the beginning of the study to measure their science process skills. The hypotheses were tested by using analysis of covariance (ANCOVA) and two-way analysis of variance (ANOVA). The results indicated that instruction based on constructivist approach caused a significantly better acquisition of scientific conceptions related to chemical bonding and produced significantly higher positive attitudes toward chemistry as a school subject than the traditionally designed chemistry instruction. In addition, science process skill was a strong predictor in understanding the concepts related to chemical bonding. On the other hand, no significant effect of gender difference on understanding the concepts about chemical bonding and students&amp / #65533 / attitudes toward chemistry as a school subject was found.

The purpose of this study was to explore the effects of CCTIA over TDCI for 9th grade students&rsquo / understanding of chemical bonding concepts. Also, the effect of instruction on students&rsquo / attitude toward chemistry as a school subject and the effect of gender difference on understanding of chemical bonding concepts and attitudes toward chemistry were investigated. The subjects of this study consisted of 41 ninth grade students from two classes of a chemistry course in TED Ankara High School. This study was conducted during the 2003-2004-spring semester. The classes were randomly assigned as control and experimental groups. Students in the control group were instructed by TDCI whereas students in the experimental group were instructed by CCTIA. CBCT was administered to both groups as a pre-test and post-test in order to assess their understanding of concepts related to chemical bonding. Students were also given ASTC as a school subject at the beginning and end of the study to determine their attitudes and SPST at the beginning of the study to measure their science process skills. At the end of the study, we administered interviews to the students. The hypotheses were tested by using ANCOVA and ANOVA. The results revealed that CCTIA caused a significantly better understanding of scientific conceptions related to chemical bonding concepts than the TDCI. In addition, these two modes of instruction developed the similar attitude toward science as a school subject. Also, science process skill was a strong predictor in understanding the concepts related to chemical bonding. Alternatively, no significant effect of gender difference on understanding the concepts about chemical bonding and on students&rsquo / attitudes toward chemistry as a school subject was found.